Typical motor vehicles operate by complex mechanical and electromechanical linkages between the driver, or operator, of the vehicle, and the principal components of the motor vehicle, such as the engine and brakes. Efforts to reduce costs and weight of motor vehicles have made it incumbent upon motor vehicle designers to create alternative means of control for the vehicles, which would reduce materials, reduce weight, and enhance safety features.
One alternative to mechanical and electromechanical control systems is known as “by-wire” technology. In by-wire technology, the operator inputs control of the motor vehicle through an interface, typically pedals in the case of brake or throttle controls. The inputs are then transmitted to the underlying controls by electronic or electromagnetic means, rather than by mechanical or electromechanical means.
Through the incorporation of by-wire technologies, motor vehicles no longer require cumbersome mechanical and electromechanical linkages, which results in several advantages. For example, since mechanical linkages are generally bulky and heavy, utilization of by-wire technology has the potential to reduce weight and provide more cabin space. Further, by-wire technology also allows for a more standardized driver control interface, as there is no need to accommodate variations in mechanical linkage packages due to different engines, transmissions and other major components. Additionally, by incorporating microprocessors into the design, additional analysis and control may be added between the driver input and the brake or throttle actuation.
As a result, it is seen that by-wire technology provides an opportunity to redesign and improve driver interfaces. The brake pedal of motor vehicles has received the most attention of these control systems due to the critical nature of this application. Traditionally, the design of the human interface with the braking system has been a subjective endeavor. With the advent of a Brake Feel Index (BFI) as reported in SAE technical paper 940331 “Objective Characterization of Vehicle Brake Feel”, a method was developed to correlate objective engineering parameters to these subjective assessments. In the case of BFI, such aspects as pedal application force, pedal travel and pedal preload are compared to desired response. These parameters were determined to match the characteristics of vehicles with mechanical and electromechanical linkages that the drivers were accustomed to for each class or type of vehicle involved.
The operative characteristics of by-wire brake pedals are represented, generally, by U.S. Pat. Nos. 6,186,026; 6,298,746; 6,330,838; 6,367,886; 6,464,306; and 6,591,710. Of particular interest of these is U.S. Pat. No. 6,186,026 which discloses a flexible cantilever pedal lever with an affixed sensor, wherein flexure control is provided by a stationary reaction surface which interacts with the flexure of the pedal lever as driver foot force is applied to foot pad (or pedal pad), wherein the reaction surface contour is tuned to provide emulation the feel of a traditional pivoting brake pedal.
These prior art by-wire brake pedal concepts have the potential to give fuel consumption reduction through mass saving as well as cost saving, but have a number of deficiencies that need to be overcome to enable their wide-spread implementation. For example, the pedal lever is structurally weak at the springy section, which can adversely impact operation of the pedal in the event of off-center application of applied force loads to the foot pad (that is, where pedal torque is present). Also, the pedal lever can lose springiness due to wear, which can cause degraded functionality, especially in the case of panic braking, where excessive loads may be applied to the brake pedal. Further, the prior art by-wire brake pedal concepts do not contain fine flexure control features. In this regard, while known prior art by-wire brake pedals may enable adjustment of the feel of coarse flexure control (i.e., U.S. Pat. No. 6,186,026), there remains the need for provision of fine flexure control.
Accordingly, what remains needed in the art is a cantilever control system, adaptable for by-wire systems, which provides fuel savings from material reduction and overcomes the prior art issues of structural weakness particularly as regards off-center loading, failsafety, excessive loading, and facility for both coarse and fine flexure control.